# Program to restore the array from adjacent pairs in Python

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Suppose we have a 2D array called adPair of size n-1 where each adPair[i] has two elements [ui, vi] represents that the elements ui and vi are adjacent in an array called nums, in nums there are n unique elements. We have to find the array nums. If there are multiple solutions, return any of them.

So, if the input is like adPair = [[3,2],[4,5],[4,3]], then the output will be [2,3,4,5]

To solve this, we will follow these steps −

• my_map := an empty map to store list for different keys
• for each pair (a, b) in adPair, do
• insert b at the end of my_map[a]
• insert a at the end of my_map[b]
• for each key a and value list l in my_map, do
• if size of l is same as 1, then
• nums := a list with two elements (a, l)
• come out from loop
• for i in range 1 to size of adPair - 1, do
• a, b := my_map[last element of nums]
• if a is same as second last element of nums, then
• insert b at the end of nums
• otherwise,
• insert a at the end of nums
• return nums

## Example

Let us see the following implementation to get better understanding −

from collections import defaultdict
my_map = defaultdict(list)
for a, b in adPair:
my_map[a].append(b)
my_map[b].append(a)

for a, l in my_map.items():
if len(l) == 1:
nums = [a, l]
break
for i in range(1, len(adPair)):
a, b = my_map[nums[-1]]

if a == nums[-2]:
nums.append(b)
else:
nums.append(a)

return nums

print(solve(adPair))
[[3,2],[4,5],[4,3]]

[2, 3, 4, 5]